Removed deprecated context receivers

[babisRoutis]

Closes #223

[babisRoutis]

@dzarras low priority, but please take a look

[dzarras]

In many instances methods that were defined as:

context(Raise<E>)
fun Receiver.f(param1: P1, param2: P2): Result { }

have been rewritten as

fun Raise<E>.f(receiver: Receiver, param1: P1, param2: P2): Result { }

I feel like such methods should have been rewritten instead as:

fun Receiver.f(param1: P1, param2: P2): Either<E, Result> { }

For me f() remains an extension function of Receiver. What changes, is how we communicate the errors we produce.

@babisRoutis What do you think? I feel like this approach would produce more comprehensive and readable code.